The miniaturization of electronic circuits, such as, for example, microchips or storage structural units as well as micromechanical components and microfluid components, has been continuously advancing for decades. In order to further increase the density of these functional groups, stacking of such devices was begun some years ago. The functional groups are produced for this purpose on a substrate, for example a wafer. The wafers are then aligned with one another and bonded with one another, which in some few process steps leads to a large yield and primarily functional groups stacked on one another in a high density.
The functional groups of different wafers in most cases also have different functionalities. Thus, the functional groups of a first wafer can be microchips, while the functional groups of the second wafer can be memory chips. Before the actual connecting process, an alignment of the wafers with one another is carried out. The smaller the functional groups on the wafers, the more precise the alignment process of two wafers with one another must be in order to achieve the necessary precision and a correspondingly low scrapping.
The precision with which two wafers can be aligned with one another depends decisively on the optical and the mechanical component parts of the alignment unit, as well as the use thereof.
In the case of the optical component parts, it is primarily to be ensured that the magnification, but especially the resolution, is high enough to detect the alignment marks on the substrates as exactly as possible. In addition, as large as possible a depth of focus area in the case of a correspondingly high magnification and resolution is desirable.
In the case of mechanical components, primarily the motors and the bearings are of decisive importance. The motors must accelerate, move and brake high loads, but in this case they must also allow a positional control that is as precise as possible and primarily reproducible. In order to guarantee this, special types of bearings are necessary. The bearings provide for the storage of the load that is to be shifted is as friction-free as possible. Up until now, air bearings were preferably used, which allowed a non-contact shifting of two components relative to one another.
Primarily in a vacuum environment, it may be advantageous to eliminate as many motors as possible and thus also the necessary storage in order to increase the precision and reproducibility of the remaining motors.
In the state of the art, there already exist alignment systems such as, for example, those disclosed in AT405775B. The latter show, however, some serious drawbacks. In this respect, the traveling distances between the lower and upper specimen holders in the Patent Specification AT405775B are very long, which can lead to a correspondingly inaccurate positioning of the two substrates relative to one another, when the actual joining process is carried out.
In addition, it is desirable to perform the alignment process in a vacuum environment. The use of the above-mentioned air bearings is accordingly difficult and problematic.
Therefore, another alignment system was disclosed in the publication PCT/EP2013/062473. In this publication, the problem of the long traveling distances is solved in that the substrates that are aligned with one another move laterally along the connecting axis of two markings. In contrast to the embodiment in AT405775B, the optics were not applied in front of the substrates but rather laterally thereto, so that the traveling distances can be drastically reduced. By the radical shortening of the traveling distances, the alignment unit in PCT/EP2013/062473 can use completely different motors and bearings that are primarily suitable for the vacuum.
It is therefore the object of this invention to provide a device and a method for aligning and bringing substrates into contact, with which a more precise and more efficient alignment and contacting of substrates, in particular under vacuum, is made possible.
This object is achieved with the features of claims 1 and 8. Advantageous further developments of the invention are indicated in the subclaims. All combinations that consist of at least two of the features indicated in the specification, the claims and/or the figures also fall within the framework of the invention. In the case of the indicated value ranges, values lying within the above-mentioned limits are also disclosed as boundary values and can be claimed in any combination.